Linearity of transmitters that convert baseband signals into radio frequency (RF) signals for transmission is important in band-limited communication systems. Nonlinear behavior in the transmitters causes the transmitted power of signals having amplitude modulation components to leak outside a frequency band allocated to the signals. The leakage of power outside of the allocated frequency band, and especially into adjacent channels, is referred to as adjacent channel power leakage (ACPL). ACPL is usually defined as a ratio of average power in an adjacent channel to an average power in the allocated channel. As is known in the art, ACPL is of great importance within the telecommunications field and, in the United States, is strictly regulated by the Federal Communications Commission (FCC).
Linearity is of great importance to cellular networks that are based on digital modulation formats and in which the cellular network signals are amplitude modulated. One such digital modulation format is code division multiple access (CDMA). CDMA is one of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A CDMA-capable receiver can use the code to decode a received signal in the presence of other signals in the channel. In fact, CDMA is a “spread spectrum” technique that allows multiple users to share the same radio frequency spectrum by assigning each active user a unique code. Unfortunately, the combination of AM and transmitter non-linearity causes the transmitter to generate frequency components that corrupt adjacent channels. Therefore, ACPL should be considered and appropriately addressed in the design of the transmitter.